[LiveComponent] Improve form validation error messages in exceptions

src/LiveComponent/src/ComponentWithFormTrait.php

@@ -186,7 +186,7 @@ private function submitForm(bool $validateAll = true): void
         );
 
         if (!$form->isValid()) {
-            throw new UnprocessableEntityHttpException('Form validation failed in component.');
+            throw new UnprocessableEntityHttpException(\sprintf("Form validation failed:\n%s", implode("\n", $this->extractErrors($form, $form->getName()))));
         }
     }
 
@@ -318,4 +318,24 @@ private function clearErrorsForNonValidatedFields(FormInterface $form, string $c
             $this->clearErrorsForNonValidatedFields($child, \sprintf('%s.%s', $currentPath, $name));
         }
     }
+
+    /**
+     * @return array<string>
+     */
+    private function extractErrors(FormInterface $form, string $prefix = ''): array
+    {
+        $errors = [];
+        $label = '' !== $prefix ? $prefix : 'form';
+
+        foreach ($form->getErrors() as $error) {
+            $errors[] = $label.': '.$error->getMessage();
+        }
+
+        foreach ($form->all() as $name => $child) {
+            $childPath = '' !== $prefix ? \sprintf('%s.%s', $prefix, $name) : (string) $name;
+            array_push($errors, ...$this->extractErrors($child, $childPath));
+        }
+
+        return $errors;
+    }
 }

src/LiveComponent/tests/Fixtures/Component/FormWithCollectionTypeComponent.php

@@ -53,4 +53,10 @@ public function removeComment(#[LiveArg] int $index)
     {
         unset($this->formValues['comments'][$index]);
     }
+
+    #[LiveAction]
+    public function save(): void
+    {
+        $this->submitForm();
+    }
 }

src/LiveComponent/tests/Fixtures/Form/CommentFormType.php

@@ -17,12 +17,18 @@
 use Symfony\Component\OptionsResolver\OptionsResolver;
 use Symfony\UX\LiveComponent\Tests\Fixtures\Dto\Comment;
 
+use Symfony\Component\Validator\Constraints\NotBlank;
+
 class CommentFormType extends AbstractType
 {
     public function buildForm(FormBuilderInterface $builder, array $options): void
     {
         $builder
-            ->add('content', TextareaType::class)
+            ->add('content', TextareaType::class, [
+                'constraints' => [
+                    new NotBlank(message: 'The comment content field should not be blank'),
+                ],
+            ])
         ;
     }
 

src/LiveComponent/tests/Functional/Form/ComponentWithFormTest.php

@@ -14,6 +14,7 @@
 use Symfony\Bundle\FrameworkBundle\Test\KernelTestCase;
 use Symfony\Component\DomCrawler\Crawler;
 use Symfony\Component\Form\FormFactoryInterface;
+use Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException;
 use Symfony\UX\LiveComponent\Tests\Fixtures\Component\FormWithCollectionTypeComponent;
 use Symfony\UX\LiveComponent\Tests\Fixtures\Entity\User;
 use Symfony\UX\LiveComponent\Tests\Fixtures\Factory\CategoryFixtureEntityFactory;
@@ -488,4 +489,40 @@ public function testFormWithLivePropContainingAnEntityImplementingAnInterface()
         self::assertEquals(1, $user->id);
         self::assertEquals('Nicolas', $user->username);
     }
+
+    public function testSubmitFormExceptionMessageContainsFieldPathsAndMessages()
+    {
+        $mounted = $this->mountComponent('form_with_collection_type');
+        $dehydratedProps = $this->dehydrateComponent($mounted)->getProps();
+
+        $exception = null;
+
+        try {
+            $this->browser()
+                ->throwExceptions()
+                ->post('/_components/form_with_collection_type/save', [
+                    'body' => [
+                        'data' => json_encode([
+                            'props' => $dehydratedProps,
+                            'updated' => [
+                                'blog_post_form.title' => '',
+                                'blog_post_form.content' => 'too short',
+                                'blog_post_form.comments' => [['content' => '']],
+                            ],
+                        ]),
+                    ],
+                ])
+            ;
+        } catch (UnprocessableEntityHttpException $e) {
+            $exception = $e;
+        }
+
+        $this->assertNotNull($exception);
+        $this->assertStringContainsString('title', $exception->getMessage());
+        $this->assertStringContainsString('content', $exception->getMessage());
+        $this->assertStringContainsString('The title field should not be blank', $exception->getMessage());
+        $this->assertStringContainsString('The content field is too short', $exception->getMessage());
+        $this->assertStringContainsString('blog_post_form.comments.0.content', $exception->getMessage());
+        $this->assertStringContainsString('The comment content field should not be blank', $exception->getMessage());
+    }
 }